The invention relates to a vane pump and particularly to the profile of the contour ring around the vanes that establishes the chambers of the pump and to a precompression chamber in the pump.
Vane pumps of this type are generally known. They usually comprise a rotor having a circumferential wall with radial slots which receive vanes. The rotor rotates within a contour ring which, in a double-stroke vane pump, forms two crescent shaped delivery spaces through which the vanes run. A fluid inlet opening and a fluid outlet opening are assigned to each of these delivery spaces. The fluid to be delivered is sucked through the inlet opening into a delivery cell formed between two vanes and is later discharged again from the cell through the outlet opening.
The fluid is delivered due to the geometry of the contour ring, as the vane cell volumes become larger in the intake region and smaller in the discharge region.
In particular when such vane pumps are used in conjunction with automatic transmissions, there is a disadvantage that the air contained in the fluid, which is particularly hydraulic oil, is greatly compressed very quickly, and this leads to disturbing cavitation noises.
To avoid these noises, it has been proposed to design the contour ring so as to achieve a slight increase in pressure. However, this has a disadvantage that the increase in pressure becomes very dependent on tolerances with regard to the shape of the contour ring. Even small production related fluctuations in the course of the contour ring consequently lead to tangible changes when the pressure increases. If there is an excessive increase in pressure as a result, this again leads to cavitation noises.